This invention concerns a control choke with a balanced external sleeve and cage trim used in the production of oil and gas wells. Prior control chokes have a flow cage with pressure balancing ports therethrough disposed within a choke body for limiting the flow rate through the control choke. These flow cages typically have an external or internal sleeve reciprocable thereon for varying the number of pressure balancing ports exposed to the incoming flow stream. This arrangement allows throttling of the flow stream through the choke to obtain a desired flow rate.
As oil and gas production from higher pressure wells has developed, the need for control chokes to use in these applications has arisen. The prior control chokes described above have required larger and more expensive means for reciprocating the flow sleeves on the flow cage to throttle the flow of production fluid. The present invention provides a novel arrangement of flow sleeve and cage which eliminates pressure loading of the reciprocation means and thereby allows use of a smaller and less expensive reciprocation means.
U.S. Pat. No. 4,240,609 to G. L. Hahn et al. discloses a production choke with means for reciprocating the closure element which includes a hollow stem with a floating piston therein to substantially counterbalance the pressure forces on the stem.
U.S. Pat. No. 4,735,229 to Lancaster is an example of a control choke with a flow cage having an external sleeve disposed thereabouts which allows throttling of the flow stream through the choke. No means for counterbalancing the pressure loads on the stem are disclosed.